The mouths and feces of 253 infants aged 3-24 months were examined for the presence of Streptococcus mutans and Streptococcus sanguis. S. mutans was found in either or both oral and fecal samples of 53 children (21%); however, it was not found in either source prior to the eruption of teeth. S. sanguis was isolated from the mouth of two children without erupted teeth. Serotype c was the most prevalent, a and b were not found in any samples and five of the sampled population exhibited more than one serotype of S. mutans.